Moonstone

(moon-stohn)

HISTORY and LORE

According to the folklore of ancient India, made of crystallized moonbeams. Also linked to the moon by other cultures and the gem’s name reflects this time-honored association. One old story says if you hold a moonstone in your mouth under the light of the full moon, you’ll be able to see your future.

Birthstone for June

VALUE FACTORS

Phenomenon: Displays a glow that seems to float inside the gem. The effect is technically known as adularescence. In fine quality, it’s soft yet bright.

Color: Typically colorless, white, or gray. Can also be light yellow, orange, or brown. Most expensive is colorless with strong sky-blue adularescence.

Clarity: Usually translucent to opaque, but sometimes almost transparent.

Cut: Cabochons, carvings, and beads. In long narrow cabochons the effect often looks like a cat’s eye.

Carat Weight: Normally available in all jewelry sizes (up to 15 or 20 carats).

TREATMENT

Moonstone is among the gems for which there are no established treatments.

GEMOLOGY

Traditionally classified as a variety of orthoclase feldspar. Feldspars are a group of related minerals that account for almost half the volume of Earth’s crust. Orthoclase is a species within the group, and it’s composed primarily of potassium, aluminum, silicon, and oxygen; chemical formula KSlSi3O6.

The gem known as rainbow moonstone is a variety of labradorite feldspar. Labradorite’s chemical composition is somewhat variable, and includes calcium and sodium along with aluminum, silicon, and oxygen.

In both types, light reflecting from layers in the gem’s structure causes the special optical effect. With classic moonstone there are alternating sections of orthoclase and the fledspar known as albite. In rainbow moonstone, the layers are produced by repeated reversals of the crystal pattern.